The present invention relates to an image recorded product having a synthesized image formed by superimposing additional information on an original image, an image recording system for recording the synthesized image as a hard copy, an image reproducing system for reproducing the additional information from the recorded synthesized image and a recording medium which stores recording/reproducing procedure recorded thereon.
In recent years, image recording system, image reproducing system and so forth have been developed to be adaptable to a variety of methods in order to prevent falsification and forgery of an identification card (i.e., ID card) having a face picture or the like recorded as an image thereon, a document having a logotype or a seal impression recorded as an image thereon and another recorded product.
For example, a method in which a face picture is confirmed by a human being to specify a person is an easiest and reliable method. Thus, fact pictures are widely employed to be adaptable to certification cards, driving licenses, passports and ID cards. The foregoing method encounters a problem of forgery of an ID card. The certification cards and so forth have been arranged to prevent forgery by means of changing the face picture by employing a method of sectioning the seal into two leaves, a laminate process and an integration process by a special image recording system. However, a high-performance color scanner and a color printer can easily be obtained in recent years and combination with a personal computer has enabled forgery of a certification card having a face picture or the like to be performed.
Also the magnetic card and the IC card for use as a credit card can be forged with knowledge and technique capable of copying the magnetically recorded portion and rewriting the contents stored in the memory. Thus, even the foregoing structures are not completely safe structures. Therefore, the face picture, which is the easiest and reliable method for identifying whether or not the person having the medium is the proper owner, has been made to be more important. However, there is a risk that forgery by changing the face picture can be performed similarly to the certification card.
On the other hand, autograph is a usual method to indicate certification of the contents of a document in a usual office work. By confirming the impression, whether or not the document has been certificated by the proper person can be determined. However, the person who has received the certified document cannot easily properly determine the impression. Thus, a problem of inefficient office work must be performed. Moreover, the impression can be synthesized by combining the existing precise scanner, a printer and a personal computer. Although logotypes partially employed by a portion of companies to be used together with documents can easily be copied. There is a risk that a document having a logotype can be forged.
A variety of methods have been employed to prevent forgery and the like by superimpose-recording additional information on an original image and to reproduce the additional information superimpose-recorded on the original image. In order to prevent forgery of a hard copy, such as a certification card, the following methods are available:
(1) A method for specifying a copying machine used to record a document in accordance with an output hard copy from the color copying machine.
The foregoing method has a structure such that a small yellow dot pattern is recorded on the output hard copy. The dot pattern has a shape peculiar to the condition of the copying machine, such as the model number. The output hard copy is read by a scanner or the like and then the superimpose-recorded dot pattern is extracted and subjected to a predetermined signal process so as to specify the copying machine.
(2) A method in which additional information is superimposed on a color image as a high frequency color difference synthesized image,
The foregoing method has a structure such that additional information is encoded and a color difference component having a high spatial frequency peak corresponding to the code is superimpose-recorded on the original image. Since the color difference component having the high spatial frequency cannot easily be recognized by a human being, superimpose-recorded additional information does not substantially deteriorate the original image. Since a usual original image does not substantially have the high frequency color difference component, superimpose-recorded additional information can be reproduced by reading the recorded image and extracting the high frequency color difference component by a signal process.
(3) A method in which additional information can be reproduced only when predetermined two images are overlapped.
The foregoing method is arranged to perform pseudo level representation of an image such that two images having different level representations in specific regions are produced and the specific regions appear dark when the two images have been overlapped.
However, the foregoing methods (1) and (2) must perform complicated operations in addition to the signal process for reading the image in order to reproduce the superimpose-recorded additional information. Therefore, superimpose-recorded additional information cannot easily be reproduced. The foregoing method (3) involves a pair of two images being overlapped. If the images forming the pair are not overlapped, additional information cannot be reproduced. That is, if additional information is required to be reproduced from a plurality of images, there arises a problem in that images must be prepared to correspond to the number of the images.